Fighting with my Zenith

kopeck · Aug 31, 2012

I have a 52499D off my '47 A that I've been trying to rebuild but haven't had a whole lot of luck.

The deal is the idle adjust screw/jet doesn't have any effect of the engine. I can have it seated or 4 turns out no change.

It has been soaked in carb cleaner and a kit installed. I use compressed air to blow everything out. I also used spray cleaner as well.

I've been told it might be something stuck int he idle circuit, if that's the case what can I do do remedy the situation?

The other thing was thinking about is getting new throttle shaft bushings installed. I couldn't find that it was leaking (propane test) but there is some play.

Any pointers would be welcomed. I've rebuilt a handful of carbs but this one is driving me nuts!

K

old · Aug 31, 2012

The idle adjust screw will have little to no effect on the engine other then at a very low idle and even then you will not be likely to hear it. Also if like the carbs I have on the B/A they have no adjustment for the main jet so from what you say you seem to believe the idle adjustment should do something above a slow idle

kopeck · Aug 31, 2012

(quoted from post at 19:22:35 08/31/12) The idle adjust screw will have little to no effect on the engine other then at a very low idle and even then you will not be likely to hear it. Also if like the carbs I have on the B/A they have no adjustment for the main jet so from what you say you seem to believe the idle adjustment should do something above a slow idle

Not to sound smart but how do you adjust something that you can't even tell if it's working or not?

I'm having low speed idling issues, so it seems like that would be a place to start.

K

Dean Olson · Aug 31, 2012

Does the Tractor otherwise run well and have plenty of power? You
may not have a problem.

My Super C's run great and have lots of power but the
"adjustments" don't seem to do much. I'm a master plumber and
shade tree mechanic. I set the carb per instructions and don't mess
with them after that. Any issue's I've had after carb rebuild where
due to my inexperience.

Janicholson · Aug 31, 2012

The float level could be high enough that the engine is pulling fuel out of the main jet. If a thin wire can be passed through the Idle screw passages and it is clear to the edge of the throttle plate It could be float level. Jim

old · Aug 31, 2012

How often do you really idle an engine??? I learned years ago that high RPM matters but an idle is just that and has nothing but an engine running thing and you can not use then at an idle. Ya nice to have but high Rs and needed low Rs are nice but can be an up/down thing.

DaveLamp · Aug 31, 2012

My '47 Super A does the exact same thing after an engine rebuild which also included a carb rebuild on the Zenith. I've had it apart umpteen times with the same result. Listen to old, he has never steered me wrong. Also as Dean said, just set it at a couple of turns and be glad it runs good at idle. That is unless you LIKE tearing your hair out (been there done that!)

kopeck · Aug 31, 2012

(quoted from post at 19:49:17 08/31/12) The float level could be high enough that the engine is pulling fuel out of the main jet. If a thin wire can be passed through the Idle screw passages and it is clear to the edge of the throttle plate It could be float level. Jim

I'll try the wire bit.

You very well could be right about the float height though, I often have a hard time setting them, it's never quite a easy as the book makes it look.

I'm soaking it again, I'll try it all again in the morning.

Thanks,

K

kopeck · Aug 31, 2012

(quoted from post at 19:57:32 08/31/12) How often do you really idle an engine??? I learned years ago that high RPM matters but an idle is just that and has nothing but an engine running thing and you can not use then at an idle. Ya nice to have but high Rs and needed low Rs are nice but can be an up/down thing.

Honestly, quite a bit.

I use it for pulling carts mainly, stop and go type stuff. It idles a lot to say the least.

Now if you run at PTO speed all the time, then sure, but I use all throttle positions.

K

Janicholson · Aug 31, 2012

Setting float height is adjusting the mixture. Do not be afraid of putting it as much as 3/32 lower than spec. Also make sure there is no fuel in it. It will sink and add extra fuel if it is leaky. Jim

Hendrik · Sep 1, 2012

This may help. See link.
I substituted the carb bowl by a large glass bowl.
Setting float level

gene bender · Sep 1, 2012

Just because you can blow air thru doesent mean the passage is completely clean. On the main body you mite need to use proper size drill bit and by hand. I use a seperate small drill chuck to use small bits to clean the idle circut hol in the bottom of the main body start with a verry small and go a little larger by steps and usually will find rusty stuff on the tip of the bit then by blowing and using a mag lite i can see lite looking down the main discharge jet hole. float setting doesent seem to be your problem. I haveseveral of these carbs on the A and B,BNs that i have even have some extra carbs

old · Sep 1, 2012

Ya if doing that yes it can be a bit of a problem. A couple things to try. #1 take a propane torch do not light it and wave it around the carb and the manifold to see if you have a vacuum leak which will cause odd problems. #2 pull the idle screw all the way out and see if it will still idle. If it does then the idle circuit is clogged up and needs to be opened which you maybe able to do with spray carb cleaner and air

David G · Sep 1, 2012

Makes my fuel injection idea look better and better.

mkirsch · Sep 1, 2012

All the engineering, machine work, and tuning to set up a fuel injection system from scratch makes adjusting the float seem like child's play.

Really, it's all a matter of developing a feel for it.

Ted in NE · Sep 1, 2012

As others have said make sure all passages are clean. Float level set. How loose is the throtttle shaft in the throtle body. Between wear on the shaft & wear in the houseing bore you pull enough air in & the idle adjustment will make no difference.

kopeck · Sep 1, 2012

I've just about had it.

I soaked the carb for 2 days, pulled it out today and did pretty much everything that was suggested here.

I used some stiff wire to poke out all the passages, followed that with spray carb cleaner in each passage followed by compressed air.

I set the float per service manual, I was very, careful and got it as close to perfect as I could. Installed everything and no dripping from the carb so the needle and seat are working correctly. Idle screw is set 1 1/2 turns from being seated.

Same old story. The idle screw can be seated or 6 turns out and it runs just the same. I even took the whole screw out and it ran, a little worse but not terribly so. It did hiss quite bit, if I put my finger over the it would change a bit.

I did a leak test, even went so far as to spray the whole thing down with either, no change what so ever.

I guess the last draw is to pull the Marvel off my BN and install it on the A, see what that does.

Just because I could I reset all the valves to make sure nothing was funky there. All the cylinders read 85 pound plus or minus a pound. I went thought the mag, new cap, point and timed it back. I also replaced all the spark plugs.

I keep coming back to the carb due to it's lack of adjustment, I guess trying another know good carb will tell me something.

Thanks,

K

Janicholson · Sep 1, 2012

Lower the float level (toward the ground) so there is less fuel in the carb. Seriously, the float level is set to make it run correctly, not set correctly to make it run. Easy change and might be a miracle. Jim

kopeck · Sep 1, 2012

How much are we talking about? I did try it about an 1/8" further down and it didn't help.

Not sure if this helps but if you put the tractor under a load it seems to clean up pretty well, it's just idling that's an issue, both fast and slow.

K

Janicholson · Sep 1, 2012

The slow idle must be in the area of 500 rpm. Much higher than that and the adjustment won't work. It probably has no effect at 750. The main jet may have been enlarged. It will take a wire drill set to measure the existing jet, or just get a new main jet. 1/8 inch should make a difference. Jim

kopeck · Sep 1, 2012

(quoted from post at 21:00:09 09/01/12) The slow idle must be in the area of 500 rpm. Much higher than that and the adjustment won't work. It probably has no effect at 750. The main jet may have been enlarged. It will take a wire drill set to measure the existing jet, or just get a new main jet. 1/8 inch should make a difference. Jim

I have no idea where the cut over is but you are probably right.

That being said I highly doubt the main jet was enlarged, at least intentionally. It's been in my family for it whole life and I don't think my grandfather ever "hot rodded" anything.

It stinks, I have a parts carb that had another main just but it got pretty buggered coming out.

I think swapping carbs could be very telling. If it cleans things up there has to be some defect in the Zenith, if it doesn't then I've been chasing the wrong thing all a long. God only knows what that could be.

oldtanker · Sep 2, 2012

Before you go swapping carbs around.....check the engine timing and points settings.

Rick

kopeck · Sep 2, 2012

(quoted from post at 05:10:13 09/02/12) Before you go swapping carbs around.....check the engine timing and points settings.

Rick

I did that already. I've exhausted just about everything I can thing of at this point.

kopeck · Sep 2, 2012

Just got in from the garage.

I put the Marvel from my BN on my A. It still doesn't idle great but mid/full throttle is much improved. The idle screw in the Marvel does change how the engine runs. I should add that this carb probably could stand being rebuilt too, the needle leaks a bit and I bet it hasn't been touched in over 20 years, that being said I'm happy to leave well enough alone with it at the moment. At WOT with out any load there's still a miss every now and then but from what I've seen these small engines tend to do that, it's not like my SM that's super smooth no mater where the throttle is.

For the fun of it I stuck the Zenith on the BN. The the idles like a dream, not a miss super smooth and it did respond to the idle screw (ie turning it all the way in changed how the engine ran). Anything above idle though was crap, just like on the A.

So first off I don't think there's an idle circuit problem in the Zenith, it's something to do when it switches over to the main jet. That still leaves me wondering what the heck is going on.

The other factor here is the BN has a battery ignition and the A has a magneto. Some of the roughness at idle might be just the fact that the timing is running fully advanced as a slow speed where as the distributor advances the timing based on RPM. Just saying it's kind of hard to compare the two.

Anyway, if I could get my Zenith to perform like my Marvel I would be happy. I would still love to get it to idle better but that might be somewhat the nature of the beast.

K

Janicholson · Sep 2, 2012

The change might have cured a vacuum leak or covered gasket problem. I am glad things are improved. Sometimes warpage of white metal parts and 50+ years of exposure just can"t be fixed. Jim

kopeck · Sep 2, 2012

(quoted from post at 10:05:32 09/02/12) The change might have cured a vacuum leak or covered gasket problem. I am glad things are improved. Sometimes warpage of white metal parts and 50+ years of exposure just can"t be fixed. Jim

Well, I'm not sure I would say improved, I have one working carburetor for two tractors.

I wish I knew what to do with the Zenith. I also wish I didn't screw up my parts carb, then I would have another one to try.

I was just looking on eBay and cores are cheap either.

K

Fighting with my Zenith

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